Not sure it matters. As you progress the only thing holding you back for longer reads is fear. Long story is just like short story, but longer. As long as a reading material is providing enough challenge to stretch you skills, it should be fine. Don;t know if you are doing this, but: Had a 6th grade teacher wwho insisted that if you read a book and it didnlt have a single word or rreference you didnlt understand, the book was too easy. She also insisted tha tyu keep a notebook and jot down thjose itens and then look them up later.